How do you stop being shy around your boyfriend and actually figure out what to start a converstion about?

Well... this is a tough one because I never really had a boyfriend, only about... say... 15 crushes, but I'll try my best.
When you're single and boys come and talk to you, your hands sweat, your knees buckle and you try not to say anything that might turn him off (I know from experience... don't ask).
Well the truth is, when you are in an actual relationship, you get accustomed to your partner and you won't feel so shy. Also, you would have spent enough time with the person to know what they like an dislike, so you would surely start a discussion about some thing that you might both like... it's natural. Don't worry, everything will fall into place at the right time.